The invention disclosed herein pertains generally to transmission mechanisms, and more particularly to a transmission mechanism for a bicycle.
It is known in the bicycle art to transmit the power delivered by a rider to the pedals of a bicycle to a ground engaging wheel of the bicycle by the use of gears and shifting mechanisms. It is also known that high performance bicycles often have transmission mechanisms which include 10 to 15 different gear ratios and a derailleur mechanism which mechanically moves a chain from one gear combination to another. The purpose of these gears and shifting mechanisms is to enable the rider to rotate the pedals of the bicycle at whatever speed he chooses, but particularly to enable the rider to rotate the pedals over a relatively narrow pedal speed range. That is, the purpose of the gears and shifting mechanisms is to enable the rider to deliver power to the bicycle over a narrow pedal speed range, while the ground engaging wheel rotates over a much wider speed range. The reason for this is that the power that a human rider can generate varies sharply with pedal speed, i.e. the power-pedal speed curve of a human rider is sharply peaked. Thus, the gears and shifting mechanisms enable the rider to rotate the pedals over the relatively narrow pedal speed range at which the rider can deliver the maximum power which he can generate. The greater the number of gears and gear ratios, the greater the bicycle speed range over which the rider may continue to deliver effectively constant power to the ground engaging wheel while rotating the pedals at an almost constant pedal speed.
The use of intermittently tensioned springs for transmitting power to a ground engaging wheel of a bicycle, or for retracting the pedals of a bicycle, is also known in the bicycle art. For example, U.S. Pat. No. 4,108,459 issued to Alvigini, and U.S. Pat. No. 524,652 issued to Risinger, disclose bicycle transmission mechanisms which include springs that are intermittently tensioned by a bicycle rider, and which springs either continuously deliver power to a ground engaging wheel of a bicycle, or are used to retract the pedals of a bicycle which have been depressed from a first position to a second position.
The Alvigini patent (U.S. Pat. No. 4,108,459) discloses a spring powered bicycle. This bicycle includes a spring drum which is incorporated in a ground engaging wheel of the bicycle. The bicycle also includes a drive shaft on which the spring drum is rotatably mounted. Contained within the spring drum is a spiral spring, an inner end of which is connected to the drive shaft and an outer end of which is connected to an outer periphery of the spring drum. A free wheeling clutch is mounted on the outside face of the spring drum and has a matching section on an inside face of the ground engaging wheel.
In the Alvigini device, two shafts are rotatably mounted on the bicycle. A lever is rigidly connected to each of the shafts and a pedal is connected to each lever. The rotatable shafts are linked to the drive shaft by a oneway clutch, a set of gears, a pair of sprocket wheels, and a transmission chain. Thus when the pedals are depressed, the spiral spring is wound up. But as the spiral spring winds up it also continuously unwinds on its outer end, causing the spring drum to rotate, thereby rotating the ground engaging wheel.
The Risinger patent (U.S. Pat. No. 524,652) discloses a bicycle which includes an eccentric spring drum, and which spring drum is rotatably mounted on an axle of the bicycle. Contained within the spring drum is a cylindrical spring, a first end of which spring is connected to the spring drum and a second end of which spring is connected to the axle. The spring drum includes a ratchet portion which engages a series of wedges connected to a hub of the bicycle. The ratchet portion engages the wedges through a series of rollers. A first end of a steel strip is wound about the spring drum and a second end is connected to a set of levers, which levers may be oscillated by depressing a set of pedals connected to the levers. In use, a rider depresses the pedals, thereby rotating the spring drum in a forward direction while simultaneously tensioning the cylindrical spring. As the spring drum rotates in the forward direction, the ratchet portion engages the wedges connected to the hub, causing the hub to rotate in the forward direction. After a completion of a pedal downstroke, the spring drum is rotated in a backward direction under the influence of the tensioned cylindrical spring, causing the pedals to return to their original position.
Various transmission mechanisms which may be used in bicycles are also disclosed in the following patents: U.S. Pat. No. 96,963 issued to Repetti; U.S. Pat. No. 2,638,359 issued to Crumble; U.S. Pat. No. 1,612,739 issued to Matsumoto; U.S. Pat. No. 3,743,535 issued to Sidlauskas; U.S. Pat. No. 4,119,182 issued to Steuer; U.S. Pat. No. 3,648,809 issued to Schwerdhofer; U.S. Pat. No. 3,720,294 issued to Plamper; U.S. Pat. No. 88,238 issued to Van Anden; U.S. Pat. No. 628,249 issued to Kane; British Pat. No. 2,460 issued to Brereton et al; U.S. Pat. No. 670,608 issued to Dennis; and U.S. Pat. No. 538,324 issued to De Graff.
An ideal bicycle transmission mechanism is one which transmits to the bicycle all the power delivered by a rider of the bicycle, regardless of the bicycle speed. That is, an ideal transmission is one wherein a rider of a bicycle may choose the power which he wishes to deliver to the bicycle by rotating the pedals at a speed which corresponds to this power, and the ideal transmission will deliver all of this power to the ground engaging wheel of the bicycle. The ground engaging wheel of the bicycle may, of course, be rotating at a speed quite different from that of the pedals, and this speed may vary over a wide range. The known prior art bicycle transmission mechanisms which employ gears and shifting mechanisms are not entirely satisfactory as ideal transmission mechanisms because they tend to be cumbersome, require appreciable time for shifting, and require almost continuous shifting under rapidly varying road conditions. More importantly, these known transmission mechanisms represent only approximations to the ideal transmission mechanism because they provide only a finite number of discrete gear ratios rather than a continuous spectrum of gear ratios.
Accordingly, a primary object of the present invention is to provide an apparatus which more nearly approximates an ideal transmission mechanism.
Apparatus for transmitting power from a driving device or power source, such as a rider of a bicycle, to a driven device, such as a ground engaging wheel of a bicycle, according to the present invention, includes a frame (for example of a bicycle), an axle which is rigidly connected to the frame, a wheel (for example, a ground engaging wheel of a bicycle) which is rotatably mounted with respect to said axle, and a driver member which is rotated by the driving device. In addition, the apparatus preferably includes an elastic element, such as a spring, which stores energy delivered by the driving device to the driver member, a reversing mechanism which transmits, in reverse, a rotational motion of the driving device to the elastic element in order to cock the elastic element, and a mechanism which allows the driving device to periodically compress and release the elastic element. The apparatus also preferably includes a free-wheeling clutch, i.e. an overriding clutch, which intermittently transmits the energy stored in the elastic element to the driven member.
In a first preferred embodiment of the present invention, which embodiment is applicable to a bicycle transmission, the elastic element includes a cylindrical spring which encircles an axle of a bicycle, a first end of which spring is connected to the axle. The free-wheeling clutch includes a ratchet wheel which is rigidly connected to a ground engaging wheel of the bicycle. Rotatably mounted on the axle is a pawl mount which includes at least one pawl which periodically engages the ratchet wheel. A second end of the cylindrical spring is connected to the pawl mount.
The mechanism which allows a rider of the bicycle to periodically compress the elastic element includes a tubular member projecting from the pawl mount, which tubular member has an inner surface with at least one shoulder. A cam, which is rigidly mounted on said axle, is encircled by said tubular member.
The driver member includes a driver which is rotatably mounted on the axle. The driver is linked to the rider of the bicycle by a set of sprockets, a reversing mechanism which includes a figure-eight transmission chain, and a pair of pedals and cranks. The driver member also includes at least one ball bearing which is rotated over the surface of the cam by the driver, and which bearing periodically engages the at least one shoulder in the inner surface of the tubular member.
In a second preferred embodiment of the present invention, which second embodiment is also applicable to a bicycle transmission, the elastic element also includes a cylindrical spring which encircles an axle of a bicycle. A first end of this spring is mounted in a semi-circular notch in a spring-mount provided on the axle. The free-wheeling clutch includes a clutch cam which is rotatably mounted on the axle. A second end of the cylindrical spring is mounted in a semi-circular notch in the clutch cam. The clutch cam carries four clutch rollers which may frictionally engage an inner surface of a hub of a ground engaging wheel of the bicycle.
The mechanism which enables a rider of the bicycle to periodically compress the elastic element includes a driver cam which is rigidly mounted on the axle adjacent to the clutch cam. An outer surface of the driver cam includes two slots, or depressions. Two rollers, which rollers are referred to as the driver cam rollers and which rollers ride over the surface of the driver cam, are connected to a tubular member which projects from the clutch cam.
The driver member includes a sprocket mount which is rotatably mounted on the axle adjacent to the driver cam. The sprocket mount is linked to the rider of the bicycle by a set of sprockets, a transmission chain, and a pair of pedals and cranks. The reversing mechanism, which is interposed between the sprocket mount and the driver cam, includes a ring gear which is rotatably mounted on the sprocket mount. A tubular member projecting from the ring gear, called a cam driver, has an internal surface with four shoulders which may engage the driver cam rollers. The reversing mechanism further includes three planet gears rotatably mounted on pins projecting from the driver cam, which planet gears engage the ring gear. A sun gear, which is rigidly mounted on a tubular member projecting from the sprocket mount, engages the planet gears.
In a third preferred embodiment of the present invention, which is similar to the second embodiment, the elastic element, the clutch cam, the driver cam, and the cam driver are mounted on the axle of the bicycle. The components of the reversing mechanism are housed in a pedal hub and are mounted on a rotatable shaft, on which rotatable shaft the cranks of the bicycle are mounted.